1. Field of the Invention
This invention relates to machines for forming a plurality of spaced openings through a stack of sheets adjacent one edge of the stack in preparation for binding the sheets through the openings; and in one aspect to such a machine which forms a plurality of spaced nonlinear slots through such a stack of sheets with the slots starting from the edge surface of the stack.
2. Description of the Prior Art
One common method for binding a stack of paper sheets is to use a machine to form a plurality of openings through a stack of sheets adjacent one edge of the stack, and to subsequently position a device through the openings to bind the sheets together.
Preferably a machine for forming such openings should form the openings simultaneously, should accommodate a relatively thick stack of sheets and should form openings of a shape which afford secure engagement with a binding device to be inserted through the openings. Also, preferably the device should be able to form the openings despite previous bindings on the edges of the sheets, which bindings may include glue, staples, stitching or hard covers.
Conventional punching machines can be used for forming circular openings which provide good engagement of the binding device with the stack. Normally, however, such machines are limited to forming openings in relatively thin stacks of sheets unless multiple punching operations are performed.
U.S. Pat. No. 3,357,280 describes a machine for forming a series of circular openings in relatively thick stacks of sheets via the use of a plurality of hollow drill bits. However, the presence of materials such as glue from previous bindings might tend to plug the hollow drill bits.
U.S. Pats. Nos. 427,931 and 1,105,056 both describe a machine for forming openings adjacent an edge of a stack of sheets by sawing slots into the stack starting from the edge surface with rotary or reciprocating saw blades. While such machines could presumably saw such slots to form openings in relatively thick stacks of sheets, they can only form linear slots which may not afford the degree of engagement with a binding device that is desired.
U.S. Pat. No. 1,980,267 describes a machine which can form a plurality of spaced nonlinear T-shaped openings along and starting from an edge of a stack of sheets. The machine described in U.S. Pat. No. 1,980,267, however, requires a sequence of sawing and piercing operations to form the openings. The piercing operation might limit the thickness of a stack of sheets in which the openings can be formed. Also the piercing operations do not form openings of sufficient width to receive many types of binding elements.